Effect of positive end-expiratory pressure levels on splanchnic perfusion and intra-abdominal pressure: a prospective clinical-experimental study in lung-healthy patients.

High levels of airway pressure and especially positive end-expiratory pressure (PEEP) have been reported to reduce splanchnic perfusion and consequently lead to organ damage. We evaluated the effect of increasing PEEP levels on splanchnic perfusion and intra-abdominal pressure in a prospective clinical-experimental trial. In 20 neurosurgical patients, who were admitted to ICU due to the risk of postoperative complications, we measured the renal and splenic Doppler resistance index (RRI and SRI), intra-abdominal pressure (IAP), and the venous impedance index (VII) at different levels of PEEP (5 to 15 cmH2O) using a non-invasive ultrasound technique. Twenty patients were included in the final analysis. All RRI and SRI values remained within the reference range throughout the protocol, with low measurement variability (SD: RRI 0.06; SRI 0.09; VII 0.22). As PEEP levels increased from 5 to 15 cmH₂O, peak and plateau pressures rose significantly, while driving pressure remained constant. Differences between PEEP levels were not significant for IAP (η2G = 0.011, p = 0.298), RRI (η2G = 0.034, p = 0.253), SRI (η2G = 0.008, p = 0.719), or VII (η2G = 0.015, p = 0.070). No significant correlations with PEEP were found for RRI (r =-0.179, p = 0.081) or SRI (r = -0.130, p = 0.205). Mean arterial pressure was stable (84 ± 11 mmHg) and did not correlate with RRI (r = 0.195, p = 0.106), but correlated with SRI (r = 0.250, p = 0.037) and IAP (r = 0.275, p = 0.022). Exploratory mixed-effects models suggested a modest effect of PEEP on RRI (-0.002, p = 0.036) and a significant effect on VII (-0.007, p = 0.003), though patient-specific factors dominated the variance (R2c = 0.60-0.91). In our cohort of mechanically ventilated, hemodynamically stable, non-fluid-responsive, healthy patients, we found no effect of increasing PEEP levels on intra-abdominal pressure or surrogates of splanchnic perfusion, but an increase in renal venous drainage at higher PEEP levels; these findings warrant confirmation in larger samples. The study was registered in the German clinical trials register (DRKS-ID: DRKS00023895 on 15.02.2021).